A large number of platinum catalyst compositions are already known for application as catalysts of the hydrosilylation reaction. Among the known platinum catalyst compositions, the platinum-alkenylsiloxane complex catalyst compositions afforded by the reaction of alkenyl-functional siloxane and a platinum compound, e.g., chloroplatinic acid, have particularly high catalytic activities and are useful as catalysts of the hydrosilylation reaction (refer to Japanese Patent Publication (Kokoku) Number Sho 42-22924 (22,924/1967)). However, large amounts of chlorine-containing impurities remain in the platinum complex catalyst compositions afforded by this preparative approach--even when a post-reaction neutralization treatment is carried out. These chlorine-containing impurities cause various problems, such as poisoning of the catalytic reaction and corrosion of surrounding equipment and materials.
Methods directed to ameliorating these problems have also already been proposed. For example, Japanese Patent Publication (Kokoku) Numbers Sho 46-28795 (28,795/1971) and Sho 55-423 (423/1980) teach platinum-alkenylsiloxane complex catalyst compositions that have a reduced content of residual chlorine-containing impurities. These compositions are obtained by causing a neutralizing agent to be present in the reaction between the alkenyl-functional siloxane and chloroplatinic acid. The platinum-alkenylsiloxane complex catalyst compositions afforded by these procedures do provide an inhibition of corrosion of the surroundings and also provide some degree of improvement in the catalytic activity. Unfortunately, the alcohol compound that is present in these platinum-alkenylsiloxane complex catalyst compositions causes undesirable secondary reactions. In particular, the use of these compositions as catalysts of the hydrosilylation reaction is accompanied by the occurrence of such problems as the production of alkoxy groups by a dehydrogenation reaction, a reduction in catalytic activity, and a reduction in storage stability.
Methods that both solve the problems associated with chlorinated impurities and prevent the secondary reactions due to the above-mentioned alcohol compounds have also been examined. In this vein, for example, Japanese Patent Publication (Kokoku) Numbers Sho 46-28795 and Sho 55-423 also teach methods for the high-purity preparation of platinum-alkenylsiloxane complexes by evaporating off the solvent from the platinum-alkenylsiloxane complex catalyst composition. In a departure from other heretofore known methods, Japanese Patent Publication (Kokoku) Number Hei 2-53102 (53,102/1990) teaches a method for the very high-purity preparation of a platinum complex with the same structure. This method involves first mixing a Pt(0)-bis(cyclooctadiene) complex with vinyldisiloxane and subsequently evaporatively eliminating the cyclooctadiene. The platinum catalyst compositions afforded by these methods are highly active and also provide suppression of the reactions secondary to hydrosilylation that are caused by the presence of impurities in the catalyst composition. However, the isolation of these high-purity platinum complexes necessitates a step in which the volatile components are completely removed, and this step itself requires the high-yield recovery of small amounts of a high-viscosity material. In addition, the commercial execution of these methods is highly problematic from an economic point of view. In general, the application of a platinum complex catalyst composition as a hydrosilylation catalyst requires dilution of the composition with solvent or reaction medium prior to its addition to the reaction system, but the high-purity platinum complex catalyst compositions under consideration become unstable when brought into solution, resulting in problems such as rapid decomposition even at room temperature with the production of platinum black and a decline in catalytic activity.
Japanese Patent Publication (Kokoku) Number Hei 3-36573 (36,573/1991) also teaches a method for the preparation of a highly catalytically active platinum catalyst composition for use as a hydrosilylation catalyst. This method, which uses chloroplatinic acid and divinyltetraorganodisiloxane as starting reagents, involves a lengthy reaction under heating until the divinyltetraorganodisiloxane in the system has disappeared due to reaction. The platinum catalyst composition afforded by this method has a high catalytic activity and is easy to handle due to the relatively low viscosities involved. However, the appearance of this platinum catalyst composition ranges from dark brown to black, and it causes product discoloration even when added to the reaction system in just the small amounts required for a catalyst. In addition, platinum black is produced during storage, which results in changes in the catalytic activity during storage.
The present inventors achieved the present invention as a result of extensive investigations directed to solving the problems described above. In specific terms, the object of the present invention is to provide a high-purity platinum complex catalyst composition that is very stable to storage and has a high catalytic activity, a process for the preparation of this composition, and a microparticulate thermoplastic resin catalyst composition.